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T96                                        FERRO-SILICON

magnesia mixture. The covered crucible is heated for about an hour in
a good bunsen flame and then for about half an hour in a blowpipe flame.
When cold, the solid cake is placed in a porcelain dish, the crucible
being washed first with water and then with hydrochloric acid, the latter
being then gradually added until the ferric and magnesium oxides are com-
pletely dissolved (10 grams of the mixture require about 45 c.c. of HC1 of
D 1-12). The liquid is afterwards evaporated to dryness and treated fur-
ther as in the preceding method.

2.  Determination of the Carbon.—With products not attacked by
acids, the carbon should be estimated by direct combustion in a current of
oxygen (see Iron, I, b).

3.  Determination of the Manganese.—(a) The hydrochloric  acid
solution obtained in the determination of the silicon as under i, a or i, b is
placed in a measuring flask.   The residue remaining after treatment of the
silica with hydrofluoric and sulphuric acids is dissolved in hydrochloric
acid or, if insoluble matter then remains, fused with sodium carbonate and
the fused mass dissolved in hydrochloric acid.    This solution is added to
the other in the measuring flask, the whole made up to volume and the
manganese titrated by Volhard's method (see Ferro-manganese).

(b) In presence of chromium or vanadium, 0-2-2 grams of the sample
are fused with a mixture of sodium carbonate and magnesium oxide (see
I, b) and the product lixiviated with hot water (if the mass is green owing to
the presence of manganates, these are reduced by addition of a small quantity
of sodium peroxide, excess of which is decomposed by boiling for some time).
The residue is collected on a filter, washed with hot water, dissolved in
cone, hydrochloric acid, boiled to expel chlorine, and, when cool, made up
to volume in a 250 c.c. measuring flask : in an aliquot part the manganese
is estimated by Volhard's method (see Ferro-manganese).

4.  Determination of the Phosphorus.—(a) An aliquot part of the
hydrochloric acid solution obtained after elimination of the silica (see i,
a and b) is concentrated to a syrup and the phosphorus precipitated with
the molybdate reagent (see Determination of phosphorus in iron).

(b} 1-3 grams of the sample are fused with the sodium carbonate-
magnesia mixture (see i, b), the product being dissolved in hydrochloric
acid and the silica rendered insoluble and removed. The solution is then
evaporated to dryness, the residue dissolved in nitric acid and the phosphoric
acid precipitated with the molybdate reagent.

5.  Determination of the Sulphur.—1-3 grams of the sample are
fused with sodium carbonate and magnesia (see i, b}, the mass taken up
in bromine water, the bromine expelled by boiling, hydrochloric acid added
to dissolve the ferric oxide and magnesia, the silica rendered insoluble,
the residue taken up in dilute hydrochloric acid and, the silica having been
removed, the sulphuric acid formed precipitated in the filtrate with barium
chloride (see Gravimetric determination of sulphur in iron).

* *

The more common, commercial ferro-silicons have the following percentages
of silicon: 20/25, 25/3°. 5°/6o, -75 and 80/90 ; those with the higher propor-
tions are the more valued,by addition of a little tartaric